The probe was launched in light of the Chinese government's "apparent failure to comply with the January 15, 2020" agreement, said the US trade envoy's office, and Washington could take further action in response.

The move "underscores the Trump Administration's resolve to hold China to its Phase One Agreement commitments," said US Trade Representative Jamieson Greer.

But it could further inflame tensions between the world's two biggest economies, with temperatures again rising in Trump's second presidency.

Trump has imposed sweeping duties on US partners since returning to the White House this year, and Washington and Beijing have engaged in tit-for-tat retaliation.

At one point, tariffs on both sides reached triple digits, snarling supply chains. While both sides have de-escalated tensions, their truce remains shaky.

Washington has previously threatened to enforce China's compliance with the "Phase One" trade deal inked in 2020, which saw Beijing pledge to boost purchases of US products and services by hundreds of billions of dollars over 2020 and 2021.

But the target was not met amid the Covid-19 pandemic.

Among industries, China had pledged to step up purchases of US agricultural goods.

But fresh tensions this year saw Beijing hike tariffs on US agriculture products, including soybeans, hitting a key support base of Trump.

Chinese buyers also halted new soybean orders from the US autumn harvest, battering the sector.

On Friday, Greer vowed to protect US farmers, ranchers and workers.

"Five years following entry into force, China's lack of compliance with the Phase One Agreement appears to have undermined the conditions of competition for US companies seeking to trade with and operate in China," the USTR's office said in its notice.

In its next steps, the USTR is expected to call for comments to be submitted.